The present invention relates to mufflers for exhaust gases or the like which have a sound component, such as are typically produced by an internal combustion engine. More particularly, the present invention relates to internal combustion engine mufflers which include a sound absorbing or sound-energy dissipating material such as fiber glass.
I have previously discovered that a muffler can be constructed in which the sound or noise component in an exhaust stream is dissipated, in part, by causing reflection of the sound component through deflected and swirling streams of gas passing through the muffler. Thus, in addition to the sound dissipating effect of the sound absorbing material in the muffler, the combustion gases also act to deaden various sound frequencies found in the gases and to cooperate in the overall noise reduction achieved in the muffler. Such a muffler construction is shown in my prior U.S. Pat. No. 3,710,891.
While the muffler of U.S. Pat. No. 3,710,891 is highly effective in dissipating sound energy in exhaust gases without undesirably increasing the back pressure in the exhaust stream, certain manufacturing problems have been encountered which affect muffler life. One of the key aspects of the muffler of U.S. Pat. No. 3,710,891 is the provision of a flat plate partition or abutment or a cup-shaped partition which extends laterally across the incoming stream of gases and deflects gases and their sound component laterally and rearwardly toward sound absorbing material in the muffler. Such partitions or abutments are conventionally mounted in a perforated tube or channel-defining means into which exhaust gases are discharged in a stream, usually through a Venturi nozzel.
If the angular relationship between the stream of exhaust gases and the plate or cup-type partition is exactly perpendicular, the exhaust gases will be evenly deflected laterally over 360.degree. about the longitudinal axis of the stream of gases. As a practical matter, however, the partition or abutment is seldom exactly perpendicularly aligned with respect to the stream of incoming gases. An angular misalignment of even one or two degrees will produce highly preferential flow, that is, deflection of the gases toward one side of the muffler. Such preferential flow resulting from partition or abutment misalignment in turn causes an undesirably high volume of high temperature and velocity of gases to impringe upon the sound absording material positioned proximate the periphery of the muffler casing. It has been found, therefore, that such preferential flow will cause premature breaking down and degradation of the sound absorbing material, with the result that the muffler has a useful life which is shortened by this erosion. In extreme cases, preferential flow will also cause such elevated temperatures in the sound absorbing material and casing as to produce buckling and or burnout of the internal structure of the muffler and/or the casing wall.